Chair back

ABSTRACT

An office chair ( 10 ) is provided-having a contoured back assembly ( 24 ) comprising a back frame ( 23 ) and a suspension fabric ( 26 ). The fabric is attached to the back frame through a spline ( 58 ) wherein the back frame has a three-dimensional contoured shape formed by overlapped frame rings with the fabric being joined thereto by a spline. The back frame has a split upright section to increase the ability of the left and right halves of the frame to articulate relative to each other. Further, a bayonet connection is provided between the back frame and a support upright which bayonet connection holds together the upper ends of two separate uprights of a tilt control mechanism.

CROSS REFERENCE TO RELATED APPLICATION

This application claims the benefit of U.S. Provisional Application No.60/657,313, filed Mar. 1, 2005.

FIELD OF THE INVENTION

The invention relates to an office chair with an improved chair back andmore particularly, to a chair back with a peripheral frame and asuspension fabric secured thereto.

BACKGROUND OF THE INVENTION

Preferably, conventional office chairs are designed to providesignificant levels of comfort and adjustability. Such chairs typicallyinclude a base which supports tilt control assembly to which a seatassembly and back assembly are movably interconnected. The tilt controlmechanism includes a back upright which extends rearwardly and upwardlyand supports the back assembly rearwardly adjacent to the seat assembly.The tilt control mechanism serves to interconnect the seat and backassembly so that they may tilt rearwardly together in response tomovements by the chair occupant and possibly to permit limited forwardtilting of the seat and back. Further, such chairs typically permit theback to also move relative to the seat during such rearward tilting.

The back assembly of such office chairs may have a variety ofconstructions wherein one type of construction includes an annular backframe which defines an open interior in which the chair occupant's backis supported. This central open area is enclosed by a suspension meshwhich spans the opening and has the outer peripheral edge thereofaffixed to the annular frame.

The back frame further has a section thereof rigidly connected to anupright of the chair. The upright is connected to a tilt controlmechanism, which mechanism supports the seat assembly and governsrearward tilting of the upright. As such, the back assembly moves incombination with the upright when the occupant reclines within thechair.

It is an object of the invention to provide an office chair having achair back arrangement which is improved relative to prior chair backconstructions.

Therefore, the invention relates to an office chair and moreparticularly, to the construction of a chair back assembly and themounting of this chair back assembly to an upright.

The back assembly comprises an annular frame having a suspension fabricwhich spans the central opening of the back and has the periphery of thesuspension fabric connected to the frame. Preferably, the suspensionfabric comprises a single layer of suspension material which connects tothe frame by a plastic spline that is press fitted into an annularspline channel formed about the periphery of the back frame.

The back frame is defined by side frame rails, which extend vertically,and transverse cross rails, which extend horizontally between the siderails at the top and bottom thereof. The back frame has a contouredshape wherein the side frame rails curve rearwardly and outwardly in theside-to-side direction, while the cross rails also curve in thefront-to-back direction to provide a contoured shape for the back framethat comfortably conforms to the chair back of the chair occupant.

To form the spline channel, the back frame is constructed of moldedfront and back ring sections which are grooved about their respectiveperipheries to define front and rear channel portions. The front channelportion defines the front wall of the spline channel while the rearchannel portion defines the rear channel wall. The front and rear ringsections overlie each other in opposing relation and are rigidly securedtogether by suitable fastening means such as ultrasonic welding,adhesives or even threaded fasteners. When the two frame sections arerigidly joined together, the grooved portions align with each other anddefine the spline channel. In this manner, complex contours may beformed in a molded back frame while still permitting the formation of aspline channel about the periphery thereof.

Once the frame is assembled, the suspension fabric is fastened to theframe by a spline which is press fitted into the spline channel andtraps the edge portions of the suspension fabric within this channel.

The back frame also has an upright frame column which extends into thecentral opening of the chair and terminates at its upper end intransverse support arms which extend outwardly and are rigidly affixedto the middle of the side frame members to thereby provide furthersupport to the back frame. The lower end of the support column rigidlyjoins to the upright while the remainder of the support column has avertically elongate slot which separates the support column into leftand right halves. Since the back frame flexes during use as a result ofloads applied thereto when the occupant leans against the back assembly,this separation slot provides for increased independent movement of theupper corners of the chair back relative to the other.

The lower end of the support column also includes an improved bayonetconnection which rigidly joins the back frame to the uprights.

In particular, the uprights are formed as independent arms which areeach independently connected to the tilt control mechanism and movetogether in unison. The rearmost ends of the uprights are disposedadjacent to each other and define a connector hub with an upward openingsocket into which the bayonet connector is slidably inserted. Eachupright defines one-half of the socket and includes ribs projecting intothe socket that are then slidably received within a correspondingtapered slot of the bayonet connector wherein this connector slot of thebayonet connector serves to hold the rear ends of the upright sidewardlytogether and prevent separation thereof. A further fastener is providedvertically between the upright hub and the back frame to draw thesecomponents vertically together such that the separate uprights arerigidly held together by the bayonet connector and as such move togetherin unison.

The foregoing features provide an improved back frame arrangement,wherein other objects and purposes of the invention, and variationsthereof, will be apparent upon reading the following specification andinspecting the accompanying drawings.

BRIEF DESCRIPTION OF THE DRAWINGS

FIG. 1 is a front elevational view of an office chair having aninventive back assembly arrangement.

FIG. 2 is a side elevational view of the office chair.

FIG. 3 is a rear isometric view thereof.

FIG. 4 is a front isometric view thereof.

FIG. 5 is a side view of a back assembly.

FIG. 6 is a front view thereof.

FIG. 7 is an exploded isometric view of the back assembly with afastener for mounting the back frame on the tilt control mechanism ofthe chair.

FIG. 8 is an enlarged exploded view of the mounting section of the backframe.

FIG. 9 is an exploded isometric view of the back components forming theback assembly.

FIG. 10 is a side cross-sectional view of the back assembly as takenalong the centerline of the back assembly.

FIG. 11 is a rear view of the back frame.

FIG. 12 is a front view of the back frame.

FIG. 13 is a diagrammatic view illustrating the manufacture of sheets ofsuspension fabric from a stock material.

FIG. 14 is a top cross-sectional view of a side frame member as takenalong line 14-14 of FIG. 6.

FIG. 15 is a side cross-sectional view of the top frame member as takenalong line 15-15 of FIG. 6.

FIG. 16 is a side cross-sectional view of the bottom frame member astaken along line 16-16 of FIG. 6.

FIG. 17 is a front view of a cushion adapted for mounting to the backassembly over the suspension fabric.

FIG. 18 is an exploded isometric view of the cushion components.

FIG. 19 is an enlarged side cross-sectional view of the bottom framemember with a bayonet connection along with a pelvic support membermounted to the bottom frame member.

FIG. 20 is an enlarged, partial front view of the back frame.

FIG. 21 is a rear view of the pelvic support.

FIG. 22 is a side view of the pelvic support.

FIG. 23 is a side cross-sectional view of the pelvic support.

FIG. 24 is an enlarged partial isometric view of the back assembly, seatassembly and tilt control mechanism.

FIG. 25 is an enlarged rear view of the bayonet connector.

FIG. 26 is an enlarged side view of the bayonet connector.

FIG. 27 is a top cross-sectional view of the bayonet connector as takenalong line 27-27 of FIG. 26.

FIG. 28 is a top cross-sectional view of the bayonet connector as takenalong line 28-28 of FIG. 26.

FIG. 29 is an interior side view of a support upright.

FIG. 30 is a front view of the upright.

FIG. 31 is a top cross-sectional view of a hub section of the upright astaken along line 31-31 of FIG. 29.

FIG. 32 is a top cross-sectional view of the hub section as taken alongline 32-32 of FIG. 29.

FIG. 33 is a top cross-sectional view of the bayonet connector seatedwithin a socket defined by a hub of the uprights.

FIG. 34 is an exploded isometric view of the second embodiment of a backassembly.

FIG. 35 is a top cross-sectional view of the back frame of the secondembodiment of FIG. 34.

FIG. 36 is an isometric view of the suspension fabric assembly forcovering the back frame.

FIG. 37 is a front view of a spline adapted for attachment to asuspension fabric of FIG. 36.

FIG. 38 is a top view of a first spline section.

FIG. 39 is a top view of a second spline section.

Certain terminology will be used in the following description forconvenience and reference only, and will not be limiting. For example,the words “upwardly”, “downwardly”, “rightwardly” and “leftwardly” willrefer to directions in the drawings to which reference is made. Thewords “inwardly” and “outwardly” will refer to directions toward andaway from, respectively, the geometric center of the arrangement anddesignated parts thereof. Said terminology will include the wordsspecifically mentioned, derivatives thereof, and words of similarimport.

DETAILED DESCRIPTION

Referring to FIGS. 1-4, the invention generally relates to an officechair 10 which includes various inventive features therein whichaccommodate the different physical characteristics and comfortpreferences of a chair occupant and also improve the assembly of thechair 10.

Generally, this chair 10 includes improved height-adjustable armassemblies 12 which are readily adjustable. The structure of each armassembly 12 is disclosed in U.S. Provisional Patent Application Ser. No.60/657,632, filed Mar. 1, 2005, entitled ARM ASSEMBLY FOR A CHAIR, whichis owned by Haworth, Inc., the common assignee of this presentinvention. The disclosure of this patent application is incorporatedherein in its entirety by reference.

The chair 10 is supported on a base 13 having radiating legs 14 whichare supported on the floor by casters 15. The base 12 further includesan upright pedestal 16 which projects vertically and supports a tiltcontrol mechanism 18 on the upper end thereof. The pedestal 16 has apneumatic cylinder therein which permits adjustment of the height orelevation of the tilt control mechanism 18 relative to a floor.

The tilt control mechanism 18 includes a control body 19 on which a pairof generally L-shaped uprights 20 are pivotally supported by their frontends. The uprights 19 converge rearwardly together to define a connectorhub 22 on which is supported the back frame 23 of a back assembly 24.The structure of this tilt control mechanism is disclosed in U.S.Provisional Patent Application Ser. Nos. 60/657,541, filed Mar. 1, 2005and 60/689,723, filed Jun. 10, 2005, both entitled TILT CONTROLMECHANISM FOR A CHAIR, and U.S. Provisional Patent Application Ser. No.60/657,524, filed Mar. 1, 2005, entitled TENSION ADJUSTMENT MECHANISMFOR A CHAIR, which applications are owned by Haworth, Inc. Thedisclosure of each of these patent applications is incorporated hereinin its entirety by reference.

The back assembly has a suspension fabric 25 supported about itsperiphery on the corresponding periphery of the frame 23 to define asuspension surface 26 against which the back of a chair occupant issupported.

To provide additional support to the occupant, the back assembly 24 alsoincludes a lumbar support assembly 28 which is configured to support thelumbar region of the occupant's back and is adjustable to improve thecomfort of this support. The structure of this lumbar support assembly28 and pelvic support structure is disclosed in U.S. Provisional PatentApplication Ser. No. 60/657,312, filed Mar. 1, 2005, entitled CHAIR BACKWITH LUMBAR AND PELVIC SUPPORTS, which is also owned by Haworth, Inc.The disclosure of this patent application is incorporated herein in itsentirety by reference.

Additionally, the chair 10 includes a seat assembly 30 that defines anupward facing support surface 31 on which the seat of the occupant issupported.

More particularly as to the back assembly 24, the back assembly 24 isgenerally illustrated in FIGS. 5-7. The back frame 23 comprises a pairof vertical side frame rails 35, a top frame rail 36, and a bottom framerail 37 which are joined together at the upper corners 38 of the backassembly 24 as well as the lower corners 39 to define an annular orendless frame having a central opening 40.

As can be seen in FIGS. 5-7, the back frame 23 has a contoured shapewhich ergonomically supports the back of the user. In particular, theside rails 35 curve backwardly as seen in FIGS. 5 and 7 as well asoutwardly (FIG. 6) relative to the bottom portions of the side rails 35.Further, the top rail 36 and bottom rail 37 each have a respectivecurvature to closely conform to the curvature of a typical chairoccupant.

To support the occupant, the back assembly 24 includes the suspensionfabric 25 which is secured taughtly on the frame. Specifically, the backframe 23 includes a peripheral spline channel 42, in which is fixed theperipheral edge of the suspension fabric 25 as will be discussed infurther detail herein.

The back frame 23 also generally includes a support structure 43 towhich the side rails 35 and bottom rail 37 are rigidly interconnected.This support structure 43 comprises an upright support column 44 whichextends along the chair centerline 41 (FIG. 7) to an elevation locatedjust below the middle of the side rails 35. The upper end of the supportcolumn 44 includes a pair of support arms 45 which extend sidewardly andhave each respective outer end connected rigidly to one of the siderails 35.

The lower end of the support column 43 includes a generally L-shapedconnector flange 46 (FIGS. 5 and 7) which projects forwardly and thendownwardly into fixed engagement with the lower cross rail 37. Stillfurther, this lower column end includes a bayonet connector 49 whichprojects downwardly for rigid connection to the uprights 20 by fastenerbolt 50 and nut 51 as will be described in further detail hereinafter.

Referring more particularly to the components of the back assembly 24,FIG. 9 illustrates these components in an exploded view thereof. Inparticular, the frame 23 comprises a molded rear frame unit 55 thatincludes the support structure 44 described above as well as a rearframe ring 56 which is supported on the support arms 45 of the supportstructure 44. The back frame 24 further includes a molded front framering 57 which is adapted to be mounted to the rear frame ring 56 inoverlying relation to define the spline channel 42 about the peripherythereof. Further, the back assembly 24 includes the above-describedsuspension fabric 25 and an elastomeric spline 58.

Referring to FIGS. 11 and 12, the rear frame unit 55 comprises thesupport structure 43 and the rear frame ring 56. Both the supportstructure 43 and the rear frame ring 56 are molded simultaneouslytogether in a one-piece monolithic construction having the contouredshape described above. To facilitate molding of this contoured shapewhile still possessing the spline channel 42 mentioned above, the rearframe ring 56 and front frame ring 57 are molded separate from eachother and then affixed together.

Turning to the support structure 43, the support column 44 thereof islocated centrally within the lower half of the central frame opening 40.The support column 44 has a base end 59 and a pair of column halves 60and 61 which are separated from each other by a vertically elongatecolumn slot 62. The column 44 therefore is formed as a split column bythe slot 62 which extends along a substantial portion of the length ofthe column 44 with the column halves 60 and 61 being joined together bythe solid base section 59. As such, the column halves 60 and 61 aresupported in cantilevered relation by the base section 59. The rearframe unit 55 and front frame ring 57 are formed from a glass fillednylon material that is molded into the desired shapes wherein thismaterial has limited flexure so as to permit flexing of the variousareas of the frame when placed under load by a chair occupant. Since thecolumn halves 60 and 61 are separated from each other by the slot 62,these column halves 60 and 61 may articulate independently of each otherto facilitate flexing and movement of the various frame corners 38 and39.

The upper ends of the frame halves 60 and 61 join integrally to thetransverse arms 45. The outer ends of the arms 45 extend outwardly andare molded integral with the vertical sides of the rear frame ring 56.As seen in FIG. 12, the inside faces of the column halves 60 and 61 andthe support arms 45 have an appropriate pattern of ribbing 64 toselectively rigidify the support structure 43 while still permittingflexure thereof.

In the column base 59, this column base 59 terminates at a bottom wall65 (FIGS. 9, 10 and 12), which is formed with a bore 66 extendingvertically therethrough. The bottom wall 65 further is formed integralwith the bayonet connector 49 wherein the bore 66 extends verticallythrough this bottom wall 65 and the bayonet 49 as seen in FIG. 10. Whenjoining the back frame 23 to the chair uprights 20, the fastener 50extends upwardly from the uprights 20 as will be described in furtherdetail herein and extends through the fastener bore 66 so that itprojects vertically above the bottom column wall 65. The upper end ofthe fastener 50 is engaged by the threaded nut 51 as seen in FIG. 10 tothereby secure the back frame 23 to the uprights 20. Thisinterconnection between these components will be described in furtherdetail hereinafter.

Further as to the bottom wall 65, this wall extends forwardly to definea horizontal leg 68 of the L-shaped flange 46, which flange 46 thenturns downwardly to define a vertical leg 69 (FIGS. 5, 7 and 10). Thebottom column section 59 serves to rigidly support the bottom cross rail37 of the back frame 23. As such, the bottom frame rail 37 is morerigidly supported and has less relative movement under occupant loadsthan the middle frame areas supported by the support arms 45 or even theupper frame corners 38 which have the greatest amount ofdisplaceability. In this manner, the rear frame unit 55 provides forcontrolled flexing of the entire back frame 23.

Referring to FIGS. 11 and 12, the rear frame ring 56 comprises top andbottom ring sections 71 and 72 and left and right ring sections 73 whichextend vertically. As seen in FIG. 14, each side ring section 73includes raised connector ribs 74 and 75 as well as an additional rib 76which defines the inside end of the spline channel 42 and is alsolocated directly adjacent to a spline groove 77 that is adapted toaccommodate the thickness of the spline 58. The outer edge of the ringside section 73 includes a thinner portion 78 and essentially definesthe rear side portion of the spline channel 42.

As to the horizontal rail section 71, this rail section 71 includes aninterior rib 80, a channel rib 81 and an intermediate connector face 82.Adjacent to the channel rib 81, a spline groove 83 is provided toaccommodate the thickness of the spline 58 while the outer edge portion73 continues across the top ring section 71.

Referring to FIGS. 16 and 20, the lower rail section 72 includes aspline channel 85 along its entire lateral width so as to accommodatethe spline 58. Here again, the outer edge portion 78 continues throughthis region to define the back portion of the spline channel 42. In themiddle of the lower ring section 72, a recessed pocket 87 is definedwhich opens upwardly and is located vertically adjacent to a lockingpost 88, the function of which will be described in further detailhereinafter.

The pocket 87 is defined by side walls 89 which side walls 89 includenotches 90 at the bottom end thereof directly adjacent to the splinegroove 85. It is noted that all of the spline grooves 77, 83 and 85 arearranged in end-to-end relation so as to define a continuous groove forcontinuously accommodating the spline 58 therein. Further, the channelribs disposed directly adjacent to these spline grooves 77, 83 and 85are formed continuously in end-to-end relation.

Turning next to the front frame ring 57, this frame ring 57 has a frontface 92 which faces forwardly and a rear face 93 which faces rearwardlytowards the rear frame ring 56 and is adapted to abut thereagainst andbe fixedly secured thereto. This frame ring 57 is defined by verticalring sections 94 and a top ring section 95 and a bottom ring section 96.

As to the side ring sections 94 (FIG. 14), these ring sections 94include a rearwardly projecting connector rib 98 and an interior edgeportion 99 which are adapted to abut against and be fixedly secured tothe connector ribs 75 on the rear frame ring 56. Preferably, the frontand rear frame rings 57 and 56 respectively are joined together byultrasonic welding of these components with the faces disposed incontact being welded together. The front ring sections 94 are moldedwith a channel rib 99 disposed directly adjacent to a spline groove 100,which spline groove 100 is disposed in opposing relation with the otherspline groove 77 to define an enlarged interior portion in which thespline 58 may be received. The outer edge portion 101 of the front ring57 is disposed adjacent to but spaced apart from the other edge portion78 to thereby define the entry portion of the spline channel 42.

As to the top ring section 95 (FIG. 15), this is formed similar in thatit includes a channel rib 102 and a spline groove 103 which is disposeddirectly adjacent to the outer edge portion 101 to thereby form thespline channel 42 in cooperation with the spline groove 83 and outeredge portion 78 of the rear frame ring 56. The outer edge portion 101 ofthe front frame ring 57 furthermore extends downwardly along the othervertical ring section 93 and then across the bottom ring section 96.

The bottom ring section 96 (FIG. 16) is formed with a spline groove 105extending thereacross in alignment with the opposing rear spline groove85. In this manner, the rear frame ring 56 defines a rear portion of thespline groove 42 while the front frame ring 57 defines a front portionthereof which said frame rings 56 and 57 when disposed in opposingrelation define the channel 42 so that it opens radially outwardly andhas an enlarged interior groove in which the spline 58 and associatedfabric material may be received in non-removable engagement. As bestseen in FIG. 14, the fabric 25 is wrapped around the spline 58 toessentially define a folded hem which folded hem is then pressed intothe spline channel 42 by an appropriate tool or tooling.

In this manner, the suspension fabric 25 is tightly fitted onto the backframe 23 so that the fabric material 25 is stretched taut as generallyillustrated in FIG. 10 and then angles away from the back frame 23 andspans the central frame opening 40.

The suspension fabric 25 is formed of any suitable suspension materialwhich preferably is elasto-meric and preferably has an open weave thatprovides for breathability. FIG. 13 generally illustrates the formationof the pieces of suspension fabric 25 wherein FIG. 13 illustrates aninitial stock material 110 from which is cut multiple pieces of thesuspension fabric 25. The suspension fabric 25 preferably is formed as asingle layer but may have multiple overlying layers and may also includecushioning included therein.

In the office chair 10 of the invention, the chair 10 may be providedwith a separate cushioned pad 111 (FIGS. 17 and 18) that covers thesuspension fabric 25. The pad 111 has an upper pocket 112 and a lowerpocket 113 that are adapted to be pulled over and fitted onto the backframe 23. The pad 111 is formed as a composite pad having a rear fabriclayer 114, an intermediate cushion 115 and a front fabric layer 116which layers 114, 115 and 116 are all sewn together about theirperipheral edges.

To define the upper pocket 112, upper and lower pocket walls 117 and 118are provided which are formed of a flexible fabric material and are sewnon three sides to the adjacent peripheral edges of the composite pad111. The pad 111 is installed by first placing one of the pockets 112 or113 over the associated horizontal edge of the back frame 23 and thenpulling the other pocket vertically and fitting this on the oppositehorizontal frame edge.

More particularly as to the frame mounting pocket 87 formed in the backframe ring 56, the front side of the pocket 87 is enclosed by the frontframe ring 57. This pocket 87 is provided to support the lower end of apelvic support unit or pusher 120 which faces forwardly and is adaptedto press against the rear pelvic region of a chair occupant. Referringto FIGS. 21-23, the pelvic support 120 has an enlarged panel or pad 121that is supported on a cantilevered support arm 122. The lower end ofthe support arm 122 has a plug portion 123 which is forked to define apair of locking legs 124. The distal ends of the legs 124 include nubs125 that project sidewardly or outwardly for engagement with the notches90 formed in the pocket 87. Also the plug portion 123 includes a lockingrecess 126 which opens rearwardly and essentially is defined by a blindbore.

When the front and rear frame rings 56 and 57 are fixed together such asby welding, the support pocket 87 still opens upwardly from between theinterface between these two ring sections. This permits the plug portion123 of the pelvic support 120 to be plugged downwardly into the pocket87. During this downward insertion, the connector legs 124 deflectinwardly toward each other until the nubs 125 align with thecorresponding pocket notches and then return to their undeflectedcondition with the nubs 125 seated in the notches 90.

Since the pelvic support 120 is formed of a resiliently deflectablematerial such as plastic, the support arm 122 is able to be bentforwardly during insertion or even for removal to permit the pocket post88 to slide along the face of the pelvic support 120 until it alignswith the corresponding locking recess 126, after which the support arm122 returns to its undeflected condition with the post 88 seated withinthe recess 126. These cooperating components prevent unintentionalvertical displacement of the pelvic support 120. Since the resilientlydeflectable suspension fabric 25 lies against the front face 127 of thesupport panel 121, the fabric 25 tends to press the pelvic support 120rearwardly so that the stop post 88 is most effective in preventingremoval of the pelvic post 120. However, since the suspension fabric 25also is stretchable, the pelvic support 120 may still be bent forwardlyto permit removal of same from the support pocket 87.

Turning to the connection of the back assembly 24 to the tilt controlmechanism 19, this is accomplished through the bayonet connector 49referenced above. The tilt control mechanism 19 has two separateuprights 20 which project rearwardly from opposite sides of the chairand have their upper ends aligned in side by side relation to define theaforementioned connector hub 22. The above-described central column ofthe back assembly 24 fits into this hub 22 and rigidly holds theuprights 20 in aligned side by side relation through use of theaforementioned bolt 50.

Referring to FIGS. 25-28, the bayonet connector 49 projects downwardlyfrom a lower surface 130 of the column base 59. As seen in FIG. 25, thedownwardly projecting bayonet connector 49 has the fastener bore 66extending through the vertical length thereof. The lateral sides 131 ofthe bayonet connector 49 have a shallow taper wherein the sides 131converge inwardly downwardly. In the middle of the bayonet back face132, a vertically elongate slot 133 is provided along the entire lengthof the bayonet connector 49. This slot 133 has a bottom opening 134 andconvergent slot edges 135 which taper inwardly upwardly.

Referring to FIG. 26, the bayonet front face 136 also is taperedrelative to the back face 132 although the taper of the back face 132 isshallower than the taper of the front face 136. Hence, the bayonet 49 istapered in both the front to back plane and the side to side plane. Thelowermost corners of this front face 136 are provided with reliefs orcutouts 137.

FIGS. 27 and 28 are cross-sectional views as taken through the bayonetconnector 49. As can be seen, the central bore 66 extends verticallytherethrough. The front face 136 faces forwardly and has facets thatcurve generally sidewardly until terminating in the reliefs 137 in thebottom area thereof.

In the center portion of the front face 136, a front groove 138 isprovided between a pair of protuberances 139. When comparing FIGS. 27and 28, the groove 138 is deeper near the top of the bayonet connector49 as seen in FIG. 27 and is shallower at the lower end (FIG. 28). Theprotuberances 139 also decrease in height when comparing the top end(FIG. 27) and the lower end (FIG. 28).

As to the slot 133, this slot 133 is shallower at the lower end (FIG.28) as compared to the upper end (FIG. 27). This slot 133 as well as thegroove 138 tend to draw the upper ends of the uprights 20 sidewardlytogether and hold these ends in side by side relation. At the same time,the tapered side faces 131 and the tapered front and back faces 132 and136 facilitate a snug fit when these components are drawn together bythe bolt 50.

More particularly as to the upright 20, FIGS. 29 and 30 illustrate aleft side upright 20. The opposite right side upright 20 is formedsubstantially as a mirror image relative to the upright of FIGS. 29 and30 and hence, a detailed discussion thereof is not required.

More particularly, the front end of the upright 20 includes a hexagonalhole 141 which fits onto the end of a pivot shaft disposed within thetilt control housing 19. The opposite upright 20 also mounts onto theopposite end of this pivot shaft so that both of the uprights 20 pivotdownwardly in unison during rotation of the shaft.

The intermediate section of each upright 20 includes a seat mount 142 onwhich the back end of the seat assembly 30 is supported.

Most importantly, at the back end of the upright 20, a hub section 143is provided which defines one-half of the hub 22 mentioned above. Thehub section 143 includes a chamber 144 that has an open upper end 145and an open inner side 146. On the left side upright 20 illustrated inFIGS. 29 and 30, a locator knob 145 projects sidewardly from the insideface 146 of the hub section 143. With respect to the right side upright20, this locator knob 145 is instead replaced with a shallow locatorbore in which the knob 145 is received in tight-fitting engagement. Theillustration of the inside face of this right side upright 20 isidentical to FIG. 29 except it is a mirror image thereof wherein theillustrated knob 145 of FIG. 29 would in fact be a circular recess.

Referring to FIGS. 31 and 32, the shape of the socket section 144 has aninterior profile as illustrated in FIGS. 31 and 32 which issubstantially a negative image of the exterior profile of the bayonetconnector 49 illustrated in FIGS. 27 and 28.

More particularly, the socket section 144 has a bottom wall 150 that hasone-half of a bore 151 formed therein adjacent to the inside hub face147. When two hub sections 143 are joined side by side, the boresections 151 align sidewardly adjacent to each other to define acircular bore through which the bolt 50 passes. These bore sections 151open downwardly adjacent to a bottom wall face 152 against which thehead 153 of the bolt 50 abuts as illustrated in FIG. 19.

The socket sections 144 also each include a socket side face 155 whichtapers upwardly outwardly, and a back face 156 which also tapersupwardly outwardly. The front socket face 157 has a curved profile andtapers upwardly outwardly with a more pronounced taper as compared tothe back face 156. This front face then curves to define a projection158 that is progressively thicker in the upward direction as seen inFIGS. 32 and 31. Further, the back face 156 terminates at a central ribsection 160.

Referring to FIG. 33, when the two hub sections 143 are joined side byside to each other the two socket sections 144 are aligned sidewardly inregistry to define an upward opening socket 162 of the hub 22, and therib sections 160 essentially define a vertically elongate rib 161. Thisrib 161 slidably fits within the corresponding slot 133 of the bayonetconnector 49. Since the slot 133 is tapered, this draws the rib sections160 sidewardly together and prevents any sideward displacement of thehub sections 143 away from each other once the back assembly 24 isinstalled within the hub 22. Similarly, the projections 158 define ashallow rib 164 which fit into the groove 138 to further assist indrawing these hub sections 143 sidewardly together.

The tapered shape of the bayonet connector 49 and the correspondingsocket 162 provides for a snug fit between the opposing faces of thesecomponents. It will be understood that FIG. 33 includes some clearancespace between these spaces for diagrammatic purposes to assist in theillustration thereof but that the spacing between such surfaces is muchcloser in practice to prevent any undesirable looseness in the backassembly 24. Referring to FIG. 19, the hub 22 is generally depicted bythe bottom wall 150 thereof. During assembly, the bayonet connector 49is fitted into the socket 162 of the hub 22 and then these componentsare drawn tightly together by insertion of the bolt 50 through the bore66 and then the nut 51 is threaded thereon to place these components incompression. A Bellville washer 165 or other resilient or mechanicallocking means may be provided to prevent any loosening of the bolt 50and nut 51.

As an additional feature of this connector arrangement, this arrangementalso may be used to secure the lumbar assembly 28 in place. Referring toFIG. 10, this lumbar assembly 28 may include an upright support bracket170 having a bottom bracket wall 171. As seen in FIG. 19, this bottombracket wall 171 includes a rearward opening slot 172 to permit thebracket 170 to be slid around or straddle the bolt 50 wherein the nut 51then presses directly downwardly on this bracket wall 171 to secure thelumbar assembly 128 in place. Alternatively, as generally depicted inFIG. 7, this lumbar assembly 28 also need not be provided wherein thenut 51 would be positioned directly onto the upper face of the columnwall 65.

Hence, the bayonet connection 49 not only serves to join the bayonetconnector 49 to the hub 22, but also serves as the connector arrangementfor the lumbar assembly 28 which optionally may be installed on thischair 10.

With respect to the above-described chair 10, the back frame 24 isassembled by first joining the rear frame ring 56 to the front framering 57 by ultrasonic welding. Thereafter, the suspension fabric 25 isresiliently stretched over the back frame 23 with the peripheral edgesof the fabric 25 being affixed into the spline groove 42 by the spline58. If desired, the pelvic support 120 may be plugged into theappropriate pocket 87 formed in the bottom frame rail 37.

Thereafter, to mount the back assembly 24 to the tilt control mechanism19, the frame bayonet connector 49 is plugged into the socket 162 of thehub 22. The appropriate fastener 50 with its associated Bellville washer165 are inserted upwardly through the fastener bore 60 and then nut 51is threaded on the upper end of the bolt 50. If the lumbar assembly 28is being provided, this would then be positioned by sliding its bracket170 onto the bolt 50 after which the nut 51 would then be tightened tosecure all of these components together. In this manner, the backassembly 24 is rigidly connected to the uprights 20 and tilts rearwardlytherewith.

As an alternative to the above described frame construction, FIGS. 34and 35 illustrate a multi-component back frame 180 which comprises arear frame unit 181 and a front frame ring 182. The rear frame unit 181and front frame ring 182 are substantially similar to the componentsdescribed above and thus a detailed discussion of these components isnot believed to be required with the following discussion primarilyrelating to additional modifications to this frame construction.

In this regard, these frame components 181 and 182 would includeappropriate fastener bores 183 such that the rear frame unit 181 andfront frame ring 182 could be fastened together by screws 184. Oncethese two frame sections 181 and 182 are joined together, theyessentially define a spline groove 185 in a manner substantially similarto that described above. Thereafter, the back frame 180 also includes anelastomeric pad ring 190 which generally conforms to the shape of thefront frame ring 182 but is formed of a compressible material such as aspongy foam. FIG. 35 illustrates in phantom outline the initialcross-sectional profile of this pad ring 190 when secured to the frontframe ring 182.

The back frame 180 also includes a suspension fabric 191 that has aspline 192 sewn to its periphery by threads 193 or other suitablefastening means. This spline 192 fits into the spline channel 185 tosecure the suspension fabric 191 in place.

The suspension fabric 191 preferably is an elastomeric material which istensioned when installed. To facilitate tensioning of this suspensionfabric 191, the pad ring 190 preferably is compressed as illustrated insolid outline in FIG. 35 wherein the compression of the pad 190 adds anadditional outward biasing force to the suspension fabric 191 toincrease the tension therein. As an additional function, the pad ring190 also overlies the screws 184 and hides these components from view.

Referring to FIG. 35 as well as additional FIGS. 36-39, the spline 192also has an improved inventive construction. More particularly, thesuspension fabric 191 comprises an initial pattern of sheet material 195formed of an elastomeric fabric cut to an appropriate shape as seen inFIG. 36. The spline itself comprises two U-shaped spline sections 196and 197. Initially as seen in FIGS. 38 and 39, these spline sections 196and 197 are formed in a straight configuration with V-shaped cut-outsprovided therein. In particular, these V-shaped cut-outs facilitatebending of the spline sections 196 and 197.

Referring to FIG. 35, it is noted that the spline section has arelatively wide cross-sectional shape defined by a bulbous end portion200 and an interior edge 201. One side of the spline section 196includes slide ribs 202 while the opposite side includes a locking rib203 thereon. This locking rib 203 projects outwardly and inwardly intothe groove to tightly squeeze the material of the suspension fabricagainst the interior side wall of the spline groove 185.

Because of this wide shape, it is necessary to provide the patterns ofcut-outs to facilitate bending of this wide plastic spline piece. Moreparticularly, each of the spline sections 196 and 197 as illustrated inFIGS. 38 and 39 include first and second groups of V-shaped cut-outs205, 206, 207 and 208 which correspond to the corners of the back frame,as well as additional individual cut-outs 209. The patterns of cut-outsat the corners 205, 206, 207 and 208 provide for a significant amount ofbending while the additional individual cut-outs 209 are only needed toprovide gentle curvature.

As seen in FIGS. 36 and 37 the splines 196 and 197 initially have thecut-outs facing outwardly after which the spline sections 196 and 197are sewn directly onto the fabric material 195 by the threads 193. Thesethreads 193 pierce directly through the fabric material as well as theplastic of the spline sections 196 and 197.

To effect insertion of the spline 192 into the spline groove 185, thespline sections 196 and 197 are then flipped or folded inwardly whereinthe edge 201 initially starts at the outside of the fabric 195 as seenin FIG. 36 and then is folded inwardly so that it is seated within theinner end of the spline groove 185. The various cut-outs therefore firstserve to permit bending to the shape illustrated in FIGS. 36 and 37wherein the cut-outs are located along the outer edge and then areflipped inwardly and permits a reverse bend in the spline sections 196and 197 with the cut-outs now being located on the inside end of thespline groove 185. In this manner, the spline 192 is installed byfolding the spline inwardly and inserting same into the peripheralspline groove 185 formed in the back frame 180.

Although particular preferred embodiments of the invention have beendisclosed in detail for illustrative purposes, it will be recognizedthat variations or modifications of the disclosed apparatus, includingthe rearrangement of parts, lie within the scope of the presentinvention.

1. A chair comprising: a seat assembly; and a back assembly supportedrearwardly adjacent to said seat assembly, said back assembly comprisinga peripheral back frame which projects upwardly above said seat assemblyand defines an open area; and said back assembly further including asuspension fabric which overlies said open area and has a peripheryconnected to a corresponding periphery of said back frame, said backframe comprising front and rear frame sections which fit one over theother in facing relation and are fixed together wherein said peripheraledge of said back frame comprises a peripheral spline channel extendingabout the interface between said front and rear frame sections, saidspline channel opening outwardly and adapted to receive said peripheraledge of said suspension fabric therein, said back frame furtherincluding an elongate spline which engages said periphery of saidsuspension fabric and is press-fitted into said spline channel innon-removable engagement therewith, said front and rear frame sectionsdefining respective front and rear channel walls of said spline channelwherein said spline maintains said suspension fabric in a tautcondition.
 2. The chair according to claim 1, wherein said front andrear frame sections include opposing interior faces which define saidfront and rear channel walls.
 3. The chair according to claim 1, whereinsaid front and rear frame sections are contoured molded frames having acontour such that said opposing interior faces of said front and rearframe sections of a three-dimensional shape such that each of saidinterior faces is curved.
 4. The chair according to claim 3, whereinsaid spline is longitudinally elongate and has a uniform cross-sectionalshape.
 5. The chair according to claim 3, wherein said spline isfastened to said peripheral edge of said suspension fabric by fasteningmeans and has a generally flat cross-sectional shape laying flat againstan opposing face of said fabric.
 6. The chair according to claim 5,wherein said spline is formed of a pair of U-shaped spline sectionswhich each have an initial U-shape and are provided with corner reliefsso that said spline sections are folded over into an inverted U-shapeand said inverted spline sections are press-fitted into said splinechannel.
 7. A chair comprising: a seat assembly; and a back assemblysupported rearwardly adjacent to said seat assembly, said back assemblycomprising a peripheral back frame which projects upwardly above saidseat assembly and defines an open area; said back assembly furtherincluding a suspension fabric which overlies said open area and has aperiphery connected to a corresponding periphery of said back frame,said back frame comprising front and rear frame sections which fit oneover the other in facing relation and are fixed together wherein saidperipheral edge of said back frame comprises a peripheral spline channelextending about the outer periphery of the interface between said frontand rear frame sections, said spline channel opening outwardly andadapted to receive said peripheral edge of said suspension fabrictherein, said back frame further including an elongate spline which iscontained within an edge portion of said periphery of said suspensionfabric and is press-fitted into said spline channel in non-removableengagement therewith, said front and rear frame halves definingrespective front and rear wall sections of said spline channel whereinsaid spline maintains said suspension fabric in a taut condition; saidfront and rear frame sections being individually molded frames having athree-dimensional contour which defines opposing interior faces thatabut against each other when said front and rear frame sections arejoined together, said interior frame faces also having athree-dimensional contour such that each of said interior faces iscurved.
 8. The chair according to claim 7, wherein said interior facesabut in continuous contact with each other about the periphery of saidback frame.
 9. The chair according to claim 8, wherein said fabric isaffixed continuously about the periphery thereof to the correspondingperiphery of said back frame.
 10. The chair according to claim 9,wherein said suspension fabric is stretched to a taut condition whensaid periphery of said fabric is joined to said spline channel.
 11. Achair comprising: a seat assembly comprising a seat frame; a backassembly supported on said seat frame so as to project upwardlytherefrom, said back assembly comprising a back frame which joins tosaid seat frame and has an annular frame shape which defines an openregion that is covered by a back fabric which overlies this open region,said peripheral frame being supported on said seat frame by a columnstructure comprising an upright support column having a lower end joinedto said seat frame by a base connector such that said support column issupported in cantilevered relation with respect to said seat frame, anupper end portion of said support column including transverse columnarms which extend sidewardly from said support column and have outersideward ends which are joined to said peripheral frame intermediate theupper and lower edges of said peripheral frame, said support columnhaving separated left and right column halves which each support arespective one of said transverse arms thereon such that said columnhalves and said arms are movable separate from each other at the upperend portion of said support column while said column halves are joinedtogether at the bottom end of said support column proximate to said baseconnector, said column halves permitting separate movement of said backframe on the left and right sides thereof.
 12. The chair according toclaim 11, wherein said left and right column halves are separated fromeach other by a vertical slot extending along a major length of saidsupport column.
 13. The chair according to claim 12, wherein said columnhalves are supported in cantilevered relation by the bottom end of saidsupport column.
 14. The chair according to claim 11, wherein saidtransverse arms are joined to said peripheral frame approximately midwaybetween said upper and lower frame edges of said frame.
 15. The chairaccording to claim 14, wherein a connector web extends between thebottom edge of said back frame and said support column to restrainmovement of the bottom edge of said frame relative to the movement ofsaid upper edge of said frame.
 16. A chair comprising: a seat assemblycomprising a seat frame; a back assembly supported on said seat frame soas to project upwardly therefrom, said back assembly comprising a backframe that is joined to said seat frame by a base connector and has anannular frame shape which defines an open region which is covered by aback fabric overlying the open region, said back fabric being joined tosaid seat frame about the respective peripheries thereof so as tosupport a back of a chair occupant, wherein said base connector is abayonet connector which projects downwardly and has a tapered shapewhich tapers inwardly in the downward direction; and said seat framecomprising an upright having a front end joined to said seat frame and arearward end which extends rearwardly and joins to said bayonetconnector of said back frame, said upright comprising separate framesections on opposite sides of said chair which have respective frontends joined to said seat frame and respective rearward ends whichconverge towards each other and abut against each other to define aconnector hub, said connector hub comprising an upward opening socket inwhich said bayonet connector is slidably received and fixedly joinedthereto.
 17. The chair according to claim 16, wherein said socket isdefined partially by each of said rearward ends of said frame sections.18. The chair according to claim 16, wherein said hub has a left hubhalf and a right hub half which are defined respectively by saidrearward ends of said frame sections.
 19. The chair according to claim18, wherein said hub halves terminate at opposing inside hub faces andhave rib sections projecting inwardly into said socket at said opposinghub faces, said bayonet connection including corresponding slottedportions which extend vertically and receive said rib sections of saidhub therein to draw said hub halves sidewardly together and rigidly joinsaid frame sections together at said rearward ends thereof.
 20. Thechair according to claim 18, wherein said cooperating slots and ribs aretapered such that downward insertion of said bayonet connector drawssaid hub halves sidewardly together in close, abutting relation.
 21. Thechair according to claim 20, wherein a fastener is provided whichprojects upwardly through said hub into fixed engagement with saidbayonet connector to displace said bayonet connector downwardly intosaid socket which draws said bayonet connector and said hub verticallytogether and draws said rearward ends of said frame sections sidewardlytogether.
 22. The chair according to claim 16, wherein a fastener isprovided which projects upwardly through said hub into fixed engagementwith said bayonet connector to displace said bayonet connectordownwardly into said socket which draws said bayonet connector and saidhub vertically together and draws said rearward ends of said uprightsections sidewardly together.
 23. A chair comprising: a seat assemblycomprising a seat frame; and a back assembly supported on said seatframe so as to project upwardly therefrom, said back assembly comprisinga back frame which joins to said seat frame and has an annular frameshape which defines an open region that is covered by a back suspensionfabric which overlies this open region, said back fabric being joined tosaid seat frame about the respective peripheries thereof so as tosupport a back of a chair occupant, said back assembly further includinga cushion which is mountable on said back frame, said cushion includinga cushioned pad and pockets formed at upper and lower edges thereofwherein said upper and lower pockets fit over respective upper and loweredges of said back frame to join said cushion to said back frame, saidcushion pad overlying said suspension fabric wherein said suspension.fabric supports loads applied to said back frame by an occupant body andsaid cushion pad overlies said suspension fabric to improve the comfortof a chair occupant.